The present disclosure relates to analog-to-digital conversion and, more particularly, to an analog-to-digital converter, which is capable of enabling storage of a count value provided by a counter circuit in response to a signal level of an analog signal to be converted, and a related image sensor and analog-to-digital conversion method.
Complementary metal-oxide-semiconductor image sensor (CMOS image sensor or CIS) technology is widely used in imaging devices, such as digital cameras or mobile phones using on-board cameras. To meet the demand for high resolution and high speed imaging, a CMOS image sensor usually employs a column-parallel analog-to-digital conversion architecture to sample and convert analog signals outputted from pixels. The column-parallel analog-to-digital conversion architecture includes multiple parallel analog-to-digital converter (ADC) channels, each of which is used for converting an analog signal coming from a column of pixels. With the use of the parallel ADC channels, the column-parallel analog-to-digital conversion architecture can increase a readout speed of a large pixel array since respective analog signals outputted from different columns of pixels can be processed in a parallel manner.